1. Field of the Invention
The present invention relates to a communication control apparatus such that groups are formed by a plurality of portable information equipment and mutual communication is performed, and a method therefor.
2. Description of the Related Art
Hitherto, data transference between computers each having a communication function has mainly been performed by one-to-one communication. A most apparent typical example is data transference realized through a telephone line. To perform the communication through the telephone line, a user is needed to move to a place at which a telephone set is installed, and then instructs the telephone number intended to be communicated with. Therefore, only one-to-one communication with a person, the telephone number of which has been known, can be performed. Although use of a portable telephone results in a user being enabled to relatively freely hold communication in terms of the place for data transmission, the user is still needed to be capable of holding communication with a base station and to previously know the telephone number intended to be communicated while being limited to only the one-to-one communication.
Although broadcasting can be considered to realize one-to-multiple communication, broadcasting is able to basically realize only one directional communication.
Internet has been known to serve as a network exclusively used to realize communication among computers. Communication is realized in Internet by a technology called TCP/IP which uses IP address for specifying the terminal intended to be communicated, the IP address being address expressed by 32 bits and provided for each communication terminal. However, the communication using TCP/IP can be realized only when the communication terminals are connected by wire to one another. Thus, the foregoing communication cannot freely be used because of limitation of the places for use. Moreover, the IP address of the terminal intended to be communicated is needed to be known. In recent years, wireless LAN capable of realizing wireless computer communication has enabled the communication to be performed at arbitrary places. However, the necessity of previously knowing the IP address of the computer intended to be communicated cannot be eliminated.
As a technique capable of holding communication without the necessity of previously knowing the address of the terminal intended to be communication with, IrDA is available. IrDA is a communication technique using infrared rays and enabling data transmission to be performed simply by causing infrared-ray emitting and receiving portions of the own communication terminal to face the infrared-ray emitting and receiving portions of the communication terminal intended to be communicated. However, IrDA conveniently capable of eliminating the necessity of knowing the address of the other terminal is able to realize one-to-one communication. Thus, same information cannot be transmitted simultaneously to a plurality of persons.
As a means capable of solving the foregoing problem, a technique has been disclosed in Japanese Patent Laid-Open No. 7-336370 laid open on Dec. 22, 1995. According to the disclosure in Japanese Patent Laid-Open No. 7-336370, each communication terminal spontaneously transmits information for identifying the own communication terminal. Each communication terminal recognizes communication-enabled terminals existing adjacent to the own terminal in accordance with ID information transmitted from other communication terminals. Then, instructed communication terminals form a group in which communication terminals therein can be multicast-supplied with same information.
By employing the technique disclosed in Japanese Patent Laid-Open No. 7-336370 in a portable information device having a wireless communication function, fixed facilities are not required and multiplicity-to-multiplicity (N-to-N) communication can be performed at any place without the necessity of previously knowing the address of other communication terminals.
The technique disclosed in Japanese Patent Laid-Open No. 7-336370 eliminates the necessity of providing fixed facilities as have been required for the conventional technique and the necessity of previously knowing the address of the terminal intended to be communicated with. The technique is able to realize communication whenever a user intends regardless of the place at which the communication is held. The foregoing technique is considered to be advantageous when combined with portable information devices having the wireless communication function.
The structure disclosed in Japanese Patent Laid-Open No. 7-33637 has not particularly limited a method of setting the address of the own terminal, that is, the identifier of the own terminal. Although a conventional method may be employed in which a server for setting the identifier is provided, there arises a problem in that communication can be performed only when the server exists. As a setting method which does not use a server, a method in which a user manually sets the identifier or a method in which random numbers generated by each terminal are used may be employed. However, an excessively large identifier space is required to prevent overlap of the identifiers of adjacent terminals regardless of the time and the place. However, use of the large identifier space encounters a problem of complicated handling and deterioration in the communication efficiency.
If a plurality of communication terminal identifiers accidentally coincide with one another, the communication terminals cannot be distinguished from one another. Thus, there arises a problem in that existence of only one communication terminal is recognized though a plurality of communication terminals exist in actual.
Since the communication-enabled terminals are recognized by always transmitting ID information of the own communication terminal and receiving communication terminal ID information transmitted from other communication terminals, great electric power is required in addition to that required to transmit data. This causes a critical problem for a portable information device to arise because of limitation of electric power allowed to be provided. Since communication terminal ID information is continuously transmitted during transmission of data, data transmission band is limited.
Since communication-enabled terminal is recognized in accordance with communication terminal ID information spontaneously transmitted from each terminal, whether communication can be held with a specific terminal is required to be determined after a sufficiently long time has elapsed for the terminal to transmit the communication terminal ID information. That is, the recognition process is performed on the initiative of the terminal to be recognized as compared with the terminal which recognizes the terminal. Therefore, appropriate adaptation required by the terminal which recognizes the other terminal cannot be satisfied, thus resulting in a problem to arise in that a satisfactory efficiency cannot be realized.
On the other hand, a conventional network consisting of information communication devices A, B, C, . . . , X a s shown in FIG. 1 which are enabled to mutually transmit and receive information is arranged to transmit and receive packets by the following method.
A case will now be considered in which X is a transmitter, a terminal, to which information is intended to be transmitted, is selected from all of the terminals and information is transmitted by means of a packet having the packet structure as shown in FIG. 2. The packet consists of a data section 4 and a header section 3. The header section 3 includes two addresses, one of which is destination address 5 and another of which is transmitter address 6. When a packet of this type is transmitted in a usual network, the packet is transmitted to the address provided for the header section 3. Then, the receiving device checks the header of the supplied packet and enabled to receive the packet if the address is the own address.
If information is intended to be transmitted to one device, for example, device A, equipment address of the device A is given as described above when the packet is transmitted.
Some conventional methods to be employed when information is intended to be transmitted to a plurality of devices will now be described.
A method may be employed in which equipment address is added as all of the destination addresses similarly to the case where information is intended to be transmitted to one device, that is, one-to-one communication is repeated. Since the foregoing method has not the simultaneous information transmission function, it encounters a problem in that the number of packets to be transmitted increases if the destined devices increases and repetition of the procedure required to realize transmission results in an excessively long time being taken to complete the transmission.
Another method may be employed in which negotiation is performed between the transmitter and the receiver to set multicast address. An assumption is performed that receiving devices are devices A, B and C. Device X requires the receiving devices to set the multicast address. The multicast address determined by the transmission device X is set by the receivers, and then the receiving devices respectively return ack. When the transmission device X has received, from all of the devices A, B and C, ack indicating completion of setting of the multicast address, simultaneous information transmission is enabled. For example, Class D of IP address corresponds to this. A 28-bit group number is provided as the multicast address. Since this method requires only one packet to perform transmission, it is an advantageous method when the same information is simultaneously transmitted to a fixed device group. However, above-mentioned method needs the transmission device to require setting by transmitting, to all destined devices, a packet for requiring the negotiation formed by adding each address or the broadcast address. Since the multicast address must be changed whenever the destined device is changed, negotiation is required to determine the multicast address with a new device intended to be communicated. Therefore, there arises a problem in that an excessively long loss time involves to actually transmit data.
As a transmission method requiring only one packet without negotiation, a method is available in which equipment addresses of all transmission devices are added to the header of one packet when the packet is transmitted. However, the foregoing method involves the packet header being elongated excessively if the number of devices intended to be communicated increases, causing the overheader to be enlarged. Thus, there arises a problem in that the execution throughput is reduced.
Another method capable of transmitting information with one packet without negotiation is a method using broadcast address. The above-mentioned method enables transmission to the overall device group, to which same information can be transmitted simultaneously, to be performed while requiring a fixed header length regardless of the number of the devices intended to be communicated. Therefore, the problem of the overhead can be solved. However, the foregoing method does not permit communication with a plurality of specific devices in the device group. Thus, the method encounters a problem in that the foregoing method is repeated unintentionally.
As described above, the conventional packet transmitting and receiving method requires the transmission device to perform negotiation with the destined device to transmit information after the multicast address has been set to the transmitting device and the receiving device. Moreover, the receiving device is required to set the multicast address. Thus, the procedure has been too complicated and a long time has been required. In the case where all addresses are arranged to form an address section, increase in the addresses causes the length of the packet header to be elongated excessively. Thus, there arises a problem in that the overhead is enlarged excessively.